Electromagnetic Modeling of RE-Ba-Cu-O Coils Based Superconducting Planar Undulator and Study on Its Screening Current Induced Field

For particle accelerator-based light sources, there is ongoing interest in high-temperature superconducting (HTS) undulators utilizing Rare Earth-Ba-Cu-O (REBCO) coated conductors for their higher critical temperature (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub>) and superior critical current density (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub>) compared to Nb-Ti or Nb<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub>Sn round wires. These characteristics facilitate the development of undulators with shorter period and higher on-axis magnetic field, while also offering a larger temperature margin to accommodate the heat load. However, the screening current induced field (SCIF) and the hysteresis between the on-axis undulator field and the input current remains a significant challenge for practical applications. In this paper, we employed the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i>-formulation method to develop 2D periodic undulator models with a fixed period of 12 mm and numerically analyzed the SCIF effect on both vertical and horizontal racetrack coils-based REBCO planar undulators. Our analysis reveals that the SCIF effect can significantly distort the on-axis magnetic field, especially when the REBCO tape is wide or the undulator features a small magnetic gap. We present optimal design parameters for both types of 12 mm-period HTS undulators and provide operational guidelines concerning input currents.